, 19 tweets, 7 min read Read on Twitter
So I wrote a story for @WiredUK on #quantum computing. Amount of hype & misconceptions around it is insane!

Here's my piece: wired.co.uk/article/quantu…

(huge thnx 🙌 to all who helped: @tim_weber, @jtemperton, @where_is_chris, @MJBiercuk, @strom_m, @fcacarminati, @preskill &more)
And here is a brief summary - and some myth busting:

1. Achieving quantum supremacy *won't* magically give us super powerful supercomputers that can do everything better than standard computers;
2. Quantum supremacy simply means a quantum computer will perform *one* single task - might not be a useful task even - better than a traditional computer.

And it doesn't mean anything for any other tasks, where standard computers might & likely will be better;
3. Once a company/academic group shouts about quantum supremacy from the rooftops, the next step will be demonstrating *quantum advantage*.

That's when a quantum computer will perform a specific *useful* task better than a traditional computer;
4. Now that's when it'll start getting interesting. But for that to happen, we need to have two things:

- make better quality qubits that are as low noise as possible and with extended lifetime, and

- error-correct those qubits with special error-correcting codes;
5. At the moment, every single quantum computer in development - be it from IBM, Google, Intel, D-Wave or whatever - has very, very noisy qubits.

Noise doesn't mean they are jumping around loudly. Noise is any kind of external interference that may disturb uber-fragile...
... quantum states. Unlike familiar bits fr normal computers that can be 1 or 0, qubits can be both these values at once.

That's superposition - recall Schrodinger's cat! But any interference - heat, vibration, you name it - will disturb it & that's it, your machine is no good;
So researchers cool their quantum computers to extremely low temperatures, colder than in outer space, to help isolate the qubits from the outside world.

At least those that use integrated circuits to make their qubits, like Google, IBM, Intel, Rigetti...
Still, noise creeps through. At the moment, every single quantum computer is a NISQ.

Like the one in the video I filmed at @IBMResearch ⤵️
NISQ = Noisy Intermediate-Scale Quantum technology, meaning we are nowhere near a noise-free, error-corected quantum machine.

To overcome this hurdle, we should at least start building what's called "logical qubits" - error-corrected ones. Except they are still theoretical.
We are able to get the noise down, don't get me wrong - it's not all doom and gloom. But we can only do it for up to a dozen of physical, rather useless, qubits.
To create one single logical qubit, you need... 1000 (!!!) physical ones. Only with logical qubits we can start doing useful computations. And we are nowhere near that yet.
Others try to make qubits differently -maybe that's key here? Maybe integrated circuits approach is wrong?

There is the trapped ions method of @IonQ_Inc or @MJBiercuk (video ⤵️). It has one advantage - no need to supercool qubits as ions are quantum. But they are just as noisy!
& @Microsoft thinks it's smarter than NISQ & ions folks & working on topological qubits, 3rd approach. After years of research, it's still to make a single one. If it does, it'll be of much better quality than NISQ/ions & it'll be easier to scale.

That's Microsoft lab in Sydney:
Then there is @dwavesys D-Wave of course... But their prototype device, based on quantum annealing, based on the natural tendency of real-world quantum systems to find low-energy states, is unlikely to have fully error-corrected qubits, ever.
So where does it leave us? Can we ever build a quantum computer?? Yeah.

Can we ever achieve quantum supremacy? Very likely.

Will achieving it be useful? Probably not really, as qubits will likely still be very noisy & it'll deal w a single task, just to show that it's possible
What about all those companies shouting they're working with more and more qubits? Not too long ago 20 was the big record, now it's 49 (Intel), 50 (IBM), 72 (Google). Surely that's cool?

Well, actually, quality of qubits is way more important than quantity. & boy, are they noisy
So... Should we stop working on quantum computers? Is all the research just hype to get more money?

There's lots of hype, yeah. But we shld continue. Even w NISQ, we likely will achieve quantum advantage - & f fintech, pharma, high en physics, encryption & more it'll be crucial
We probably won't ever suppress the noise to the point of building a *universal quantum computer*.

That's what some quantum computing skeptics are quick to point out.

But that's ok - as I said, once/if we achieve quantum advantage with NISQ, that'll be a really big deal!
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